The two #4112 scrolled-mode preload browser tests asserted that the
previous-previous section (F-1) was not loaded after navigating to a section,
checking it after `waitForFillComplete()`.
The eager backward buffer (minPages) is suppressed while `#display` is
stabilizing, but pulls F-1 (and beyond) in on the first scroll events once the
fill settles. So the post-fill assertion raced the buffer: it passed locally but
failed intermittently on CI (loaded set [1,2,3,4,5]).
Assert the precondition the instant `#display` stabilizes — where the buffer is
provably suppressed and only the immediate-previous section is loaded — before
the fill settles. The eager buffer loading F-1 later is exactly what the second
test wants once it navigates back. Test-only; production behaviour is unchanged.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Huang Xin
a848c142c8